What does "ping" mean in the blogosphere?

Throughout commenting on some blogger's posts, I found that some bloggers are still unaware of how "ping" works! In short or in the layman term, "ping" is only a signal that you need to send to blog crawlers, such as Technorati, Google Blogsearch, IceRocket etc, to notify them that you have new content in your blog for them and they should fetch it ASAP!